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Variable Exhaust Nozzle?

I need one for my ducted fan but I don't have a clue where to look for one. I know BVM had one for the 255 run and Bob Fiorenze offered one. Does anyone know where I could get one for my Hurricane Cobra Jet? Looking to squeeze for some more speed!
Any info would be a help!
Thanks!

RE: Variable Exhaust Nozzle?

the fiorenze nozzles were not "functional" in terms of performance .. operation was for apearence only, and these were mounted outside of any ducting for the DF or turbine .. I had a set on a f-16 .. really nice, and i wish i knew where to get these now days ..

RE: Variable Exhaust Nozzle?

The unit on the 255 mph run (by my good friend Larry Jacob) was manufactuered by Paul Ivie (the owner and builder of the fast Ultra Viper).

I have not seen Paul in years so I do not know if he is making them any more or not. They were pretty intircate to build. I had one on my old Viper. It was powered by a big servo, tied to a small computer that sensed airspeed. The faster the model went, the more the computer closed down the nozzle.

In my experience, it did some for the top end, but it did A LOT for the low end, as you could open the nozzle up MUCH more than a standard BVM outlet size, made for very good static thrust.

I have an extra one here somewhere but I would not know where to find it. They were pretty specific to a model, not sure how hard it would be to retrofit to a Cobra.

Speaking of Cobras, I think Russ Talbot still has one in LA, there buys must have put 1000 flights on that one.

RE: Variable Exhaust Nozzle?

Thanks for some feed back!
I specifically need one for a 6" fan with a 4.5" exhaust down to about 3.15" which is about 70% squeezed. I think anything smaller would probably stall the fan blades with to much pressure in the exhaust tube.
Does anyone know how to build one?

RE: Variable Exhaust Nozzle?

I'll see if I can hunt Paul down for you. I was there for the 255 runs. It was at Best of The West years ago; using my speed traps. I know after loosing both the Ultra Viper and his back up Viper at the Saint George Utah Jet Rally years ago, Paul never did get back into flying jets. That's what marriage and children do for your pocket book. I spent a couple of years trying to beat Paul in the speed events, but to no avail. He was always just too fast. Give me a couple of days and I'll see if I can track him down for you. I'm sure he can still make the units. It wouldn't be difficult to duplicate now with microchips and diff pressure sensors being so cheap, but they ARE a lot of work. Paul's dad showed me one once in mid-assembly...simple, but lots of pieces. If you would like, send me your e-mail address and if I do get a hold of him, I'll have him e-mail you directly.

RE: Variable Exhaust Nozzle?

Thanks for the info!
It would be great if you could get in touch with him for me.
I could even just build a mechanical one that would be powered by a servo and use a variable knob switch on my extra channel to actuate the nozzle manually without any computer gizmos.
Thanks

RE: Variable Exhaust Nozzle?

Paul's nozzle was made of poly ply. It was a double layer set up with the turkey feathers on the outside and the real convergent nozzle petals on the inside. It used cables to pull the nozzle closed and used the engine thrust to open it. You could use the knob on the transmitter, but without realtime feedback, there would be no way to get the max performance out of the nozzle. The programming for the microchip would be very simple and would only require some minor testing to maximize the setup. Remember, Paul did this many years ago and technology has risen a bunch since then, so doing it without the "computer gizmos" would be a shame. I'll try to get a hold of Paul this weekend and see what he has to say. If I can't, I can probably remember enough of the setup to help you get started anyway. The other option that I had explored when Speed Runs were the thing, was making a variable inlet design for my Vortex jet. The reason the DF models run out of speed is because of the pressure drop in front of the fan unit at high speeds. As the speed increases, the thrust availabe drops off dramatically. Exhaust velocity is important, but you still have the airframe drag to overcome. The only way to do that is to apply more thrust to the airframe. With a DF model, that means choking the inlets off to allow a pressure increase by slowing the inlet velocity down before it reaches the fan, thus giving the fan more air to grab. Anyway...I'll see what I can find out.

RE: Variable Exhaust Nozzle?

Thanks for the info Dan! You are the man!
Whatever sketches or diagrams you could grab would be helpful as well since my mind is limited to making word pictures into 3D working componants.
It stems from straying from school way to early back in the day!

RE: Variable Exhaust Nozzle?

If you could mail it to me that would be fantastic!
I'll make some copies and send it right back to ya!
My computer literacy is kinda like a bat flying backwards in the sunlight if you get my drift
My address is: 11624 Shoemaker, Whittier Ca. 90605
Thanks for your help!

RE: Variable Exhaust Nozzle?

Mr. Matt, I wish all modelers were as helpful and personable as thou!
I will succeed in my quest to build "THE NOZZLE" for my Cobra!
I have all the equipment to do so (vertical mill & horizontal lathe etc...)
Once I complete "THE NOZZLE" I will need you to expound to me what I need to do to my intakes to complete the package!
I will return the plans asap!
Thanks!

RE: Variable Exhaust Nozzle?

ORIGINAL: SPEED JUNKIE

I will return the plans asap!
Thanks!

No rush, I just found another set of plans (I keep printed stuff like this as a collector), and some of the plastic parts for the nozzle. I will shoot some pics later if you think this stuff will help you you can have it.

Good luck and talk to Dan about closing the inlets, we talked about that at the field and then turbines showed up :-)

RE: Variable Exhaust Nozzle?

It's just amazing how far the technology has come. Now anyone can go 200+ if they want to. Just a few short years ago the list was very short. I wonder what it'll be like 5 years from now.
The elecronics portion sounds like fun. Once you get the nozzle build, maybe I could program a chip for you. The servo movement is incredibly easy; interface to the pressure transducer is simple. All that's needed is the algorithm for the speed curve and bingo...You've got an automatic nozzle. I'll see what the electronic component cost would be for a single unit and let you know.

Let me know if you need any other info. and I'll try to dig it up. Matt, it's amazing what you save!!! Nice going...

RE: Variable Exhaust Nozzle?

Hi !

Interesting tread..

I'm currently building a 1/9 F-14 and I'm also very interested in adding a variable exhaust nozzle.. In a recent issue of RCJI (maybe march/april 05) they told about a "functional" variable nozzle from a german "fanatic" named Manfred PrΓΆll.. Unfortunately, I haven't been able to find something more about him on the net. The article told about 20 lb thrust with nozzle opened and 30 lb when closed..

If someone have more informations (or drawings) about how to make a beautiful functional scale nozzle, post it !

RE: Variable Exhaust Nozzle?

10lbs more! don t you think it is too much increase to be true?
I can beleive that you can get more power but 20 to 30 means + 50% increase...HUGE! with afterburner spraying kero I can beleive in 30% but...here it seems a lot. If so, then lets do it right away!

RE: Variable Exhaust Nozzle?

hpghost,

I checked the magazine : they say "The PrΓΆll afterburner with nozzle closed, in reheat, will give 30 KG thrust. The PrΓΆll afterburner with nozzle open will give 20 KG thrust"

It sounds quite incredible, but with both effetcs of afterburner and variable exhaust nozzle, why not.. I'm plannig to build one for my F-14... but I'm still waiting for drawings from General Electric... []